Biochemical Studies on Human Ornithine Aminotransferase Support a Cell-Based Enzyme Replacement Therapy in the Gyrate Atrophy of the Choroid and Retina.

The gyrate atrophy of the choroid and retina (GACR) is a rare genetic disease for which no definitive cure is available. GACR is due to the deficit of ornithine aminotransferase (hOAT), a pyridoxal 5'-phosphate-dependent enzyme responsible for ornithine catabolism. The hallmark of the disease is plasmatic ornithine accumulation, which damages retinal epithelium leading to progressive vision loss and blindness within the fifth decade. Here, we characterized the biochemical properties of tetrameric and dimeric hOAT and evaluated hOAT loaded in red blood cells (RBCs) as a possible enzyme replacement therapy (ERT) for GACR. Our results show that (i) hOAT has a relatively wide specificity for amino acceptors, with pyruvate being the most suitable candidate for ornithine catabolism within RBCs; (ii) both the tetrameric and dimeric enzyme can be loaded in RBC retaining their activity; and (iii) hOAT displays reduced stability in plasma, but is partly protected from inactivation upon incubation in a mixture mimicking the intracellular erythrocyte environment. Preliminary ex vivo experiments indicate that hOAT-loaded RBCs are able to metabolize extracellular ornithine at a concentration mimicking that found in patients, both in buffer and, although with lower efficiency, in plasma. Overall, our data provide a proof of concept that an RBC-mediated ERT is feasible and can be exploited as a new therapeutic approach in GACR.

Foveoschisis associated with gyrate atrophy in ornithine aminotransferase deficiency: A case report.

Ornithine aminotransferase (OAT) deficiency is an autosomal recessive disease characterized by elevated serum ornithine levels caused by mutations in genes encoding for ornithine aminotransferase, a vitamin B6-dependent mitochondrial matrix enzyme. Gyrate atrophy (GA) is characteristic findings in OAT that characterized by sharply demarcated circular, pigmentary, brain-like areas of chorioretinal atrophy in the peripheral retina. This case report presents rare assosiation between OAT and GA and describes the characteristic imaging findings of this unique, not fully understood clinical entity. The coexistence of GA and foveoschisis is extremely rare in OAT deficiency. We report a case of foveoschisis in a patient with OAT, and we will discuss the possible mechanisms that lead to it. A 24-year-old male patient presented with complaints of decreased vision and nictalopia for 1 year. The patient, who was diagnosed with oat 6 years ago, had typical gyrate atrophy in his Fundus floresein angiography and foveoschisis in his Optical coherence tomography. He was diagnosed with gyrate atrophy and foveoschisis. GA caused by OAT deficiency may present with macular involvement in the form of foveoschisis causing central visual impairment. Ophthalmologists should not ignore detailed fundus examination in children and young patients with visual impairment and should be aware of possible systemic diseases.

Regression of treatment-resistant gyrate atrophy-associated intraretinal cystic spaces using long-term diet restriction: A case report.

PURPOSE: Gyrate atrophy of the choroid and retina (GA) is a rare genetic ophthalmologic condition which primarily manifests in childhood. It is characterized by hyperornithinemia and progressive chorioretinal atrophy. Patients may develop macular intraretinal cystic spaces (ICS) for which various treatment modalities have been reported. We report a patient who failed to demonstrate visual or anatomic improvement following multiple treatments for GA-associated ICS but showed improvement following prolonged dietary modification and vitamin supplementation. CASE DESCRIPTION: A 6-year-old male patient presented with previously undiagnosed GA associated with ICS. He received 6 consecutive monthly intravitreal bevacizumab injections as well as topical nepafenac and dorzolamide for treatment of ICS without significant change detected by optical coherence tomography (OCT) following treatment. He was also maintained on an arginine restricted diet with vitamin B6 supplementation. Over the course of the ensuing year, the patient was lost to follow-up due to the coronavirus disease 2019 pandemic. When he returned, his vision was stable, and OCT showed regression of the ICS. His mother reported that he had continued only on dietary restriction and vitamin B6 supplementation with no other medications or interventions. Plasma ornithine level measurement confirmed dietary compliance. Further follow-up showed continued stabilization of the condition. CONCLUSION: In addition to retarding progressive chorioretinal atrophy, prolonged dietary modifications may result in improvement of treatment-resistant GA-associated ICS. Parents' education on the value of dietary modifications for patients with GA is highly recommended.

A review of treatment modalities in gyrate atrophy of the choroid and retina (GACR).

Gyrate atrophy of the choroid and retina (GACR) is a rare inborn error of amino acid metabolism caused by bi-allelic variations in OAT. GACR is characterised by vision decline in early life eventually leading to complete blindness, and high plasma ornithine levels. There is no curative treatment for GACR, although several therapeutic modalities aim to slow progression of the disease by targeting different steps within the ornithine pathway. No international treatment protocol is available. We systematically collected all international literature on therapeutic interventions in GACR to provide an overview of published treatment effects. METHODS: Following the PRISMA guidelines, we conducted a systematic review of the English literature until December 22nd 2020. PubMed and Embase databases were searched for studies related to therapeutic interventions in patients with GACR. RESULTS: A total of 33 studies (n = 107 patients) met the inclusion criteria. Most studies were designed as case reports (n = 27) or case series (n = 4). No randomised controlled trials or large cohort studies were found. Treatments applied were protein-restricted diets, pyridoxine supplementation, creatine or creatine precursor supplementation, l-lysine supplementation, and proline supplementation. Protein-restricted diets lowered ornithine levels ranging from 16.0-91.2%. Pyridoxine responsiveness was reported in 30% of included mutations. Lysine supplementation decreased ornithine levels with 21-34%. Quality assessment showed low to moderate quality of the articles. CONCLUSIONS: Based primarily on case reports ornithine levels can be reduced by using a protein restricted diet, pyridoxine supplementation (variation-dependent) and/or lysine supplementation. The lack of pre-defined clinical outcome measures and structural follow-up in all included studies impeded conclusions on clinical effectiveness. Future research should be aimed at 1) Unravelling the OAT biochemical pathway to identify other possible pathologic metabolites besides ornithine, 2) Pre-defining GACR specific clinical outcome measures, and 3) Establishing an international historical cohort.

Partial regression of foveoschisis following vitamin B6 supplementary therapy for gyrate atrophy in a Chinese girl.

BACKGROUND: To report a case of genetically confirmed gyrate atrophy (GA) of choroid and retina, who showed partial regression of foveoschisis following vitamin B6 supplementary therapy. CASE PRESENTATION: A 6-year-old Chinese girl complained about night blindness and progressive decreased vision in both eyes. Her best corrected visual acuity (BCVA) was 20/63 OD and 20/100 OS. Fundus examination showed bilateral multiple, sharply demarcated, scallop-shaped chorioretinal atrophy areas in the midperipheral and peripheral of the fundus. Spectral domain optical coherence tomography (SD-OCT) showed increased central macular thickness (CMT) with multiple intraretinal cystic spaces in the both eyes. There was no leakage or staining in the macular area in late phase of fluorescein angiography (FA). Blood tests confirmed hyperornithinemia and genetic analysis revealed two heterozygous mutations on ornithine aminotransferase (OAT) gene. Based on clinical presentation and genetic test, the patient was diagnosed as GA of the choroid and retina and further treated with vitamin B6 supplementary for three weeks. Her serum ornithine levels did not change but CMT on SD-OCT declined with partial regression of intraretinal cystic spaces. Then, the patient discontinued the drug because of severe muscle pain, and foveoschisis increased to initial level a month later. CONCLUSIONS: Foveoschisis is a rare complication of GA. Vitamin B6 supplementation may alleviate foveoschisis, but its effort for reducing serum ornithine level might be limited. Potential drug adverse effects should be noted in pediatric patients.

Treatment of Intraretinal Cystic Spaces Associated With Gyrate Atrophy of the Choroid and Retina With Intravitreal Bevacizumab.

PURPOSE: To evaluate the use of intravitreal bevacizumab injections for the treatment of intraretinal cystic spaces associated with gyrate atrophy of the choroid and retina. METHODS: Retrospective chart review of 5 eyes of 3 patients with intraretinal cystic spaces associated with gyrate atrophy and treated with intravitreal bevacizumab injections was performed. Information obtained included history, examination findings, optical coherence tomography (OCT), OCT angiography, fluorescein angiography, and microperimetric findings before and after the injections. RESULTS: The mean age of patients was 11 ± 4.6 years. All patients received three monthly bevacizumab injections. The mean corrected distance visual acuity was 0.27 ± 0.10 at baseline and improved to 0.36 ± 0.12 after the injections (P = .015). The mean central macular thickness was 569 ± 127 µm at baseline and improved to 422 ± 123 µm after the injections (P = .067). Microperimetry and OCT angiography performed in 1 patient before and after the three injections showed improved macular sensitivity and vascular density measurements following the injections. CONCLUSIONS: Intravitreal bevacizumab is safe and effective in the treatment of intraretinal cystic spaces associated with gyrate atrophy. [J Pediatr Ophthalmol Strabismus. 2020;57(6):400-406.].

Cystoid macular edema secondary to gyrate atrophy in a child treated with sub-tenon injection of triamcinolone acetonide.

Purpose: Gyrate atrophy (GA) of the fundus is a rare, progressive metabolic disease secondary to the deficiency of the pyridoxal phosphate-dependent enzyme, ornithine aminotransferase. GA may lead to cystoid macular edema (CME) resulting from chronic inflammation. We aimed to report a child case with CME secondary to gyrate atrophy. Methods: Herein we presented a GA case treated with posterior sub-Tenon triamcinolone acetonide injection. Results: Optical coherence tomography examination revealed the disappearance of the macular edema that is a vision-threatening complication in GA. Conclusion: The present case showed that the posterior sub-Tenon injection of long acting steroids might be a promising treatment in CME secondary to GA.

Molecular and cellular basis of ornithine δ-aminotransferase deficiency caused by the V332M mutation associated with gyrate atrophy of the choroid and retina.

Gyrate atrophy (GA) is a rare recessive disorder characterized by progressive blindness, chorioretinal degeneration and systemic hyperornithinemia. GA is caused by point mutations in the gene encoding ornithine δ-aminotransferase (OAT), a tetrameric pyridoxal 5'-phosphate-dependent enzyme catalysing the transamination of l-ornithine and α-ketoglutarate to glutamic-γ-semialdehyde and l-glutamate in mitochondria. More than 50 OAT variants have been identified, but their molecular and cellular properties are mostly unknown. A subset of patients is responsive to pyridoxine administration, although the mechanisms underlying responsiveness have not been clarified. Herein, we studied the effects of the V332M mutation identified in pyridoxine-responsive patients. The Val332-to-Met substitution does not significantly affect the spectroscopic and kinetic properties of OAT, but during catalysis it makes the protein prone to convert into the apo-form, which undergoes unfolding and aggregation under physiological conditions. By using the CRISPR/Cas9 technology we generated a new cellular model of GA based on HEK293 cells knock-out for the OAT gene (HEK-OAT_KO). When overexpressed in HEK-OAT_KO cells, the V332M variant is present in an inactive apodimeric form, but partly shifts to the catalytically-competent holotetrameric form in the presence of exogenous PLP, thus explaining the responsiveness of these patients to pyridoxine administration. Overall, our data represent the first integrated molecular and cellular analysis of the effects of a pathogenic mutation in OAT. In addition, we validated a novel cellular model for the disease that could prove instrumental to define the molecular defect of other GA-causing variants, as well as their responsiveness to pyridoxine and other putative drugs.

Multimodal characterization of a novel mutation causing vitamin B6-responsive gyrate atrophy.

PURPOSE: Gyrate atrophy (GA) is a rare chorioretinal degeneration that results in the deterioration of night and peripheral vision, eventually leading to blindness. The disorder is caused by mutations in the gene encoding ornithine aminotransferase (OAT), causing increased levels of plasma ornithine. Treatment revolves around lowering plasma ornithine levels, with vitamin B6 supplementation being the preferred treatment. Nevertheless, most patients do not respond to this therapy. Here, we report a rare case of vitamin B6-responsive GA caused by a novel mutation in OAT and characterize the presentation with multimodal imaging. METHODS: This is a single-patient case report with a clinical diagnosis based on history, multimodal retinal imaging, laboratory findings, and DNA sequencing analysis. We include a 3D structure prediction of the novel mutant protein. RESULTS: DNA sequencing analysis demonstrated that there is a homozygous, novel variant c.473A>C: p.Y158S in OAT. Upon undergoing two weeks of vitamin B6 supplementation, the patient exhibited a 28.5% reduction in plasma ornithine levels. In a follow-up visit two years later, plasma ornithine levels were reduced by 24.1% from the levels at initial presentation and disease progression was retarded based on clinical findings. CONCLUSION: One novel homozygous missense mutation in OAT was identified and considered to be pathogenic in a patient with GA. The response for the vitamin B6 supplementation was positive, which is rare in all the GA cases reported in the literature. Our data suggests that further studies regarding the relationship between genotype and responsiveness to vitamin B6 should be conducted.

Bilateral choroidal neovascularization associated with gyrate atrophy managed with intravitreal bevacizumab.

PURPOSE: To report a case with gyrate atrophy (GA) complicated by bilateral choroidal neovascularization (CNV) treated with intravitreal bevacizumab. CASE PRESENTATION: A 20-year-old man presented with a complaint of sudden visual decrease in his both eyes. Best-corrected visual acuity (BCVA) was 20/400 and 20/500, with a spherical refractive error of -2.00 and -1.75 D, in the right and left eyes, respectively. Dilated fundus examination revealed multiple bilateral, sharply defined chorioretinal atrophy areas in the midperipheral and peripheral zone with the suspicion of CNV in both eyes. Spectral-domain optical coherence tomography revealed bilateral cystoid macular edema consistent with CNV development which was confirmed by fundus fluorescein angiography. Single dose of intravitreal bevacizumab injections were performed to both eyes of the patient. At the first month after the injection, the BCVA improved and OCT revealed scar formation without any intraretinal/subretinal fluid in both eyes. At the first-year follow-up, the maculas remained dry on the OCT and the BCVA was preserved. No additional injections were needed. CONCLUSION: Intravitreal bevacizumab might be a treatment alternative, which provides satisfactory anatomical and functional results and leads to a better central vision in cases with GA complicated by CNV.

Intravitreal ranibizumab for choroidal neovascularization secondary to gyrate atrophy in a young patient: a multimodal imaging analysis.

PURPOSE: To present a case of choroidal neovascularization (CNV) due to gyrate atrophy (GA) treated with intravitreal ranibizumab. METHODS: A 35-year-old man presented with sudden loss of vision and central scotoma in the right eye, as well as progressive night vision deterioration over the past several years in both eyes. His best-corrected visual acuity (BCVA) was 6/60 in the right eye and 6/5 in the left eye. Funduscopy revealed bilateral confluent areas of chorioretinal atrophy and optical coherence tomography showed subretinal fluid consistent with CNV development in the right eye, which was confirmed by fundus fluorescein angiography (FFA) and indocyanine green angiography (ICGA). The left eye was normal. The patient had a family history of GA. Elevated levels of plasma ornithine were detected, establishing the diagnosis. RESULTS: The patient received a regimen of 3 monthly off-label intravitreal ranibizumab injections in the right eye. At the 6-month follow-up, no subretinal fluid was noticed and BCVA was 6/48. No other injections were performed, but the patient was advised to start an arginine-restricted diet and take vitamin B6 (pyridoxine) 300 mg daily. The BCVA was preserved and chorioretinal atrophy had not progressed on funduscopy, FFA, or ICGA 1 year later. CONCLUSIONS: Intravitreal ranibizumab can offer promising anatomical and functional results, maintaining visual acuity in patients with CNV secondary to GA, especially if used in combination with arginine-restricted diet and vitamin B6 supplementation.

Gyrate atrophy of the choroid and retina with hyperornithinemia, cystinuria and lysinuria responsive to vitamin B6.

In this report, an 8-year-old girl is presented with the complaint of progressive night blindness. The authors have performed eye funduscopy, which showed chorioretinal atrophy in gyrate shape. A high level of plasma ornithine was determined. Urinary excretion of ornithine as well as lysine and cystine were increased. Patient was treated with high dose pyridoxine supplement (500 mg/dl). The night blindness condition of the patient improved. After 1 month of pyridoxine therapy ornithine level of her plasma was successfully reduced and blindness improved.

[A case of diagnosis of gyrate atrophy in infancy].

The authors describe a case of gyrate atrophy detected in a one-month baby born at 34 weeks post-conception age. Up to 2 months of life, the disease progressed--an increase in the number of foci of atrophy of the choriod and retinal pigment epithelium, there was a trend towards their fusion. The condition stabilized after the use of vitamin B6.

Macular edema associated with gyrate atrophy managed with intravitreal triamcinolone: a case report.

PURPOSE: To describe the use of 4 mg intravitreal triamcinolone acetonide (IVTA) for gyrate atrophy-related macular edema (ME) and to report anatomic and functional outcomes, during a nine-month period. CASE REPORT: A 27-year-old female complained of decreased vision since diagnosis of gyrate athrophy (GA), six years before admission. At presentation visual acuity was 20/100 in OD and 20/80 in OS. Ophthalmological examination disclosed significant cataract in OD, pseudophakia in OS and typical GA findings. Fluorescein angiography (FA) disclosed ME that was confirmed by optical coherence tomography (OCT), which also showed subfoveal fluid. OS was treated with a 4-mg IVTA injection. One month later, vision improved to 20/50+1 and foveal thickness decreased, with less leakage in FA. This picture was maintained up to six months, when there was recurrence of ME to a level similar to the baseline. At nine months, visual acuity dropped to 20/80, and ME was maintained, with remodeling in macular profile. CONCLUSION: There is a transient therapeutic effect with 4-mg IVTA injection for GA-related ME. After drug clearance, edema recurs, with return of visual acuity to pretreatment level.

Macular edema associated with gyrate atrophy managed with intravitreal triamcinolone: a case report

PURPOSE: To describe the use of 4 mg intravitreal triamcinolone acetonide (IVTA) for gyrate atrophy-related macular edema (ME) and to report anatomic and functional outcomes, during a nine-month period. CASE REPORT: A 27-year-old female complained of decreased vision since diagnosis of gyrate athrophy (GA), six years before admission. At presentation visual acuity was 20/100 in OD and 20/80 in OS. Ophthalmological examination disclosed significant cataract in OD, pseudophakia in OS and typical GA findings. Fluorescein angiography (FA) disclosed ME that was confirmed by optical coherence tomography (OCT), which also showed subfoveal fluid. OS was treated with a 4-mg IVTA injection. One month later, vision improved to 20/50+1 and foveal thickness decreased, with less leakage in FA. This picture was maintained up to six months, when there was recurrence of ME to a level similar to the baseline. At nine months, visual acuity dropped to 20/80, and ME was maintained, with remodeling in macular profile. CONCLUSION:There is a transient therapeutic effect with 4-mg IVTA injection for GA-related ME. After drug clearance, edema recurs, with return of visual acuity to pretreatment level.

OBJETIVO: Descrever o uso de acetonida de triancinolona intravítrea (TAIV) em caso de edema macular (EM) associado a atrofia girata (AG). RELATO DE CASO: Paciente de 27 anos, do sexo feminino, queixava-se de baixa de visão desde o diagnóstico de AG, há seis anos. À admissão, apresentava acuidade visual corrigida de 20/100 no OD e 20/80 no OE. Exame oftalmológico revelava catarata significativa no OD, pseudofacia no OE e achados típicos de AG. Angiografia fluoresceínica (AFG) mostrou EM, confirmado pela tomografia de coerência óptica (OCT), que também revelou líquido subfoveal. Foi então realizada injeção de 4 mg de TAIV no OE. Após um mês, a visão melhorou para 20/50+1 e a espessura foveal se reduziu, com menos extravasamento à AFG. Esse quadro foi mantido até os seis meses, quando houve recorrência do edema macular em nível semelhante ao inicial. Aos nove meses, a visão retornou a 20/80 e o edema se manteve, com remodelamento no perfil macular. CONCLUSÃO: A injeção de 4 mg de TAIV tem efeito transitório no EM associado a AG. Após a eliminação da droga, há recorrência do EM, com retorno da visão aos níveis pré-tratamento.

Prevention of ornithine cytotoxicity by nonpolar side chain amino acids in retinal pigment epithelial cells.

PURPOSE: To investigate the effect of amino acids on ornithine cytotoxicity in ornithine-delta-aminotransferase (OAT)-deficient human retinal pigment epithelial (RPE) cells as an in vitro model of gyrate atrophy (GA) of the choroid and retina. METHODS: RPE cells were treated with 0.5 mM 5-fluoromethylornithine (5-FMOrn), a specific and irreversible OAT inhibitor. OAT-deficient RPE cells were incubated with 10 mM ornithine in the presence of 20 mM of 1 of 18 amino acids or 10 mM 2-amino-2-norbornane-carboxylic acid (BCH), a conventional inhibitor of the amino acid transporter system L. Ornithine cytotoxicity and cytoprotective effects of each amino acid was evaluated with a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) colorimetric assay 72 hours after treatment with ornithine in OAT-deficient RPE cells. Ornithine incorporation into RPE cells was evaluated using DL-[14C]ornithine. RESULTS: An MTT colorimetric assay revealed that small and large zwitterionic amino acids, but not acidic or basic amino acids, decreased ornithine cytotoxicity in OAT-deficient RPE cells. Incorporation of DL-[14C]ornithine by RPE cells decreased to 79% of the control level after incubation for 48 hours with 20 mM leucine, the most effective cytoprotective amino acid. Further, BCH prevented ornithine cytotoxicity in a dose-dependent manner. Both light and heavy chains of L-type amino acid transporter (LAT)-1, LAT2, y+LAT1, and 4F2hc were expressed in RPE cells. CONCLUSIONS: The present results demonstrate that L-type amino acid transporter(s) may be involved in protection against ornithine cytotoxicity in human RPE cells. Thus, amino acid transportation in RPE cells may be a good target for a new therapy for GA as well as other kinds of chorioretinal degeneration.

Creatine corrects muscle 31P spectrum in gyrate atrophy with hyperornithinaemia.

BACKGROUND: Eye fundus destruction and type II muscle fiber atrophy in gyrate atrophy of the choroid and retina with hyperornithinaemia (GA) may be mediated by elevated ornithine concentrations which strongly inhibit creatine biosynthesis. This results in deficiency of creatine phosphate (PCr), a key intracellular energy source, as we have demonstrated in skeletal muscle of the patients by 31P magnetic resonance spectroscopy (31P MRS). MATERIALS AND METHODS: Possible correction of the relative PCr deficiency by long-term daily exogenous supplementation of creatine or its precursors was investigated in four GA patients receiving creatine and in five patients treated with guanidinoacetic acid-methionine combination. The relative PCr concentration, expressed as PCr/Pi (Pi; inorganic phosphate) or as PCr/ATP ratios, was compared with the values of untreated GA patients, and matched healthy volunteers. RESULTS: Muscle PCr/Pi ratios (mean +/- SD) of the untreated and creatine supplemented GA patients and controls were 4.9 +/- 1.4, 7.9 +/- 0.4 and 8.4 +/- 1.3. Guanidinoacetate-methionine combination was similarly effective (respective PCr/Pi ratios: 4.9 +/- 0.7, 6.3 +/- 1.1 and 10.7 +/- 2.8). CONCLUSION: Supplementation with creatine or creatine precursors almost normalised low muscle PCr/Pi ratios of patients with GA.

Genotype-phenotype correlation of a pyridoxine-responsive form of gyrate atrophy.

Two clinical subtypes of gyrate atrophy (GA) have been defined based on in vivo or in vitro evidence of response to vitamin B6 (pyridoxine), which is the cofactor of the enzyme ornithine aminotransferase (OAT) shown to be defective in GA. We identified the E318K mutation in the OAT gene, heterozygously in three patients and homozygously in one patient, all of whom were vitamin B6-responsive by previous in vivo and in vitro studies. Dose-dependent effects of the E318K mutation were observed in the homo- and heterozygotes in the OAT activity, increase of OAT activity in the presence of pyridoxal phosphate, and apparent Km for pyridoxal phosphate. The highest residual level of OAT activity and mildness of clinical disease correlated directly with the dose of the mutant E318K allele present in the patient.